Concept explainers
(a)
Interpretation:
The total vapor pressure of the solutions at
Concept Introduction:
The equilibrium between a liquid and its vapor produces a characteristic vapor pressure for each substance that depends on the temperature. The lowering of the vapor pressure is caused by a lesser ability of the solvent to evaporate, so equilibrium is reached with a smaller concentration of the solvent in the gas phase. The vapor pressure of a solution is expressed using Raoult’s law:
The vapor pressure of the solvent
Mole fraction: Mole fraction of a substance in a solution is the number of moles of that substance divided by the total number of moles of all substances present. The formula is,
Dalton’s Law:
The total pressure of a gas mixture is the sum of the partial pressures of its component gases.
Where
The partial pressure of the gas can be obtained by multiplying the total pressure of the mixture with the percent of the gases present in the mixture.
(a)

Answer to Problem 5C.11E
The total vapor pressure of the solutions at
The mole fraction of benzene in the vapor phase above the solution is
The mole fraction of toluene in the vapor phase above the solution is
Explanation of Solution
Total vapor pressure of the solution:
Given,
The vapor pressure of pure benzene at
The vapor pressure of pure toluene at
Moles of benzene is
Moles of toluene is
The mole fraction of benzene is calculated as,
Mole fraction of benzene=
Mole fraction of benzene=
Mole fraction of benzene=
The mole fraction of benzene is
The vapor pressure of benzene is calculated as,
The vapor pressure of benzene is
The mole fraction of toluene is calculated as,
Mole fraction of toluene=
Mole fraction of toluene =
Mole fraction of toluene =
The mole fraction of toluene is
The vapor pressure of toluene is calculated as,
The vapor pressure of toluene is
The total vapor pressure is calculated using Dalton’s law.
The vapor pressure of benzene
The vapor pressure of toluene
The total vapor pressure of the solution at
Mole fraction of benzene in vapor phase:
The vapor pressure of benzene is
The total vapor pressure of the solution at
The mole fraction of benzene in the vapor phase is calculated as
The mole fraction of benzene in the vapor phase above the solution is
Mole fraction of toluene in vapor phase:
The vapor pressure of benzene is
The total vapor pressure of the solution at
The mole fraction of toluene in the vapor phase is calculated as
The mole fraction of toluene in the vapor phase above the solution is
(b)
Interpretation:
The total vapor pressure of the solutions at
Concept Introduction:
Refer to part (a).
(b)

Answer to Problem 5C.11E
The total vapor pressure of the solutions at
The mole fraction of benzene in the vapor phase above the solution is
The mole fraction of toluene in the vapor phase above the solution is
Explanation of Solution
Given,
The vapor pressure of pure benzene at
The vapor pressure of pure toluene at
Grams of benzene is
Grams of toluene is
The moles of benzene is calculated as,
Moles of benzene=
Moles of benzene=
The moles of toluene is calculated as,
Moles of toluene=
Moles of toluene=
The mole fraction of benzene is calculated as,
Mole fraction of benzene=
Mole fraction of benzene=
Mole fraction of benzene=
The mole fraction of benzene is
The vapor pressure of benzene is calculated as,
The vapor pressure of benzene is
The mole fraction of toluene is calculated as,
Mole fraction of toluene=
Mole fraction of toluene =
Mole fraction of toluene =
The mole fraction of toluene is
The vapor pressure of toluene is calculated as,
The vapor pressure of toluene is
The total vapor pressure is calculated using Dalton’s law.
The vapor pressure of benzene
The vapor pressure of toluene
The total vapor pressure of the solution at
Mole fraction of benzene in vapor phase:
The vapor pressure of benzene is
The total vapor pressure of the solution at
The mole fraction of benzene in the vapor phase is calculated as
The mole fraction of benzene in the vapor phase above the solution is
Mole fraction of toluene in vapor phase:
The vapor pressure of benzene is
The total vapor pressure of the solution at
The mole fraction of toluene in the vapor phase is calculated as
The mole fraction of toluene in the vapor phase above the solution is
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Chapter 5 Solutions
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